A recent BBC news article give a short history on the canals of Mars
In the late 19th Century, the American astronomer Percival Lowell thought he saw canals on the surface of Mars.
He suggested that this was evidence that our near planetary neighbour might not only harbour life, but could possibly be home to an advanced civilisation.
This fired the public's imagination - prompting HG Wells's novel, The War of the Worlds, several comics and numerous Hollywood science fiction films depicting Martian invasions.
There was a mixture of disappointment and some relief when the existence of canals was finally disproved by orbiting spacecraft sent to the Red Planet in the 1960s and 70s.
Note: There are a number of other significant series, including John Carter of Mars and the Barsoom Series that began in 1912 by Edgar Rice Burroughs in which the canals played a major part.
If there are no canals on Mars now, what was it that everyone was seeing that created and continued the belief in the Martian Canals?